The Sun tells its readers today to vote Labour, switching sides after more than 20 years of unswerving support for the Tory party.

In a front page article headlined 'The Sun Backs Blair', the paper, which has a daily readership of more than 10 million, says Tony Blair should be the next prime minister.

The Labour leader is the 'breath of fresh air' that Britain needs, the editorial says. The Tories are 'tired, divided and rudderless' and no longer deserve support.

The paper declares: 'This is the election for the millennium. In six weeks' time, Britain will vote for a government to take it into the 21st century.

'The people need a leader with vision, purpose and courage who can inspire them and fire their imaginations. The Sun believes that man is Tony Blair.'

Editor Stuart Higgins said last night: 'This is not a decision we have taken lightly. We consider Mr Blair has all the qualities of leadership required to take this great country forward. The Tories are tired, divided and need a good rest to regroup.'

Mr Higgins told Channel 4 News that Mr Blair had many qualities similar to the Tories, but promised that the paper would remain critical of New Labour, especially on Europe.

Conservative Central Office played down the importance of the Sun 's endorsement. But only five years ago the paper boasted 'It Was The Sun Wot Won It' after John Major's victory. The Sun was responsible for a vitriolic, personalised campaign against Labour's former leader Neil Kinnock, culminating in a front page that superimposed his head on a lightbulb with the headline: 'If Kinnock wins today will the last person to leave Britain please turn out the lights'.

Sun readers were important to Mr Major in 1992, comprising more than a fifth of the electorate and more than a third of the don't knows.

Polling evidence suggests their main characteristic compared with Mirror readers is that they are less interested in politics and less committed to one party.

The paper's change of allegiance is made more striking by the fact that owner Rupert Murdoch has always taken a direct part in the decision-making at every election.

The Sun became an enthusiastic supporter of the Conservatives when Margaret Thatcher was elected leader in 1975. Attracted by her anti-union stance, it then threw its weight behind her three successive election victories.

But its support for Mr Major has waned since the ERM debacle in 1992, as Mr Murdoch has become disenchanted by the party's failure to carry on Lady Thatcher's attempts to deregulate the economy.